Reproduction Flashcards
what does DNA stand for
deoxyribonucleic acid
what is DNA
the chemical that all of the genetic material in a cell is made from
what does DNA contain
coded information of the instructions on how to put an organism together and make it work
where is DNA found
in chromosomes
what is the shape of DNA
a double helix
what causes the shape of DNA
the two strands of the DNA molecule is coiled together forming a shape of a double helix
what is gene
a small section of the DNA found on a chromosome
what do genes code tells cells to make
a particular sequence of amino acids which are put together to make a specific protein
how many amino acids are used to make thousands of proteins
20
what do genes tells cells to do
they tell them what order to put amino acids together
what do DNA determine
what proteins the cell produces e.g haemoglobin and keratin which then determines what type of cell it is
what is a genome
the entire genetic material of an organism
why is understanding the human genome a really important tool for science and medicine
1) allows scientists to identify genes in the genome that are linked to different types of diseases and inherited diseases which helps us understand them better and develop effective treatments for them
2) scientist can look at genomes to trace the migration of certain populations of people around the world, all modern humans are descended from a common ancestor who lived in Africa, but as different populations migrated away from africa, they gradually developed differences in their genomes, by investigating these differences when the new population split off in a different direction and what route they took
what are DNA strands
polymers made up of lots of repeating units called nucleotides
what do nucleotides consist of
a sugar, a phosphate group and one base
what do the sugar and phosphate groups farm
a backbone to the DNA strands
what do the bases join to make
the sugar in DNA
what are the different bases
A, T, C and G
what are the complementary base pairs
A - T
C - G
what do the order of bases determine
the order of amino acids in proteins
how are amino acids coded
by a sequence of three bases in the gene
what do the parts of the DNA that dont code for proteins do
switch genes on and off and control whether or not the gene is expressed
where are proteins made
in ribosomes
how do ribosomes make proteins
they use the code in DNA, by using a molecule called mRNA which is made by copying the code from the DNA, mRNA acts as a messenger between the DNA and the ribosome as it carries the code between the two, the correct amino acids are brought to the ribosomes in the correct order by the carrier molecule
examples of proteins
- enzymes
- structural proteins
- hormones
what do enzymes do
act as a biological catalyst to speed up the chemical reactions in the body
what do hormones do
carry messages around the body
what are structural proteins
they are physically strong proteins e.g collagen that strengthens connective tissues
what are mutations
a random change in an organisms DNA
how can the chance of mutations increase
- carcinogens
- certain types of radiation
what do mutations do
it changes the sequence of DNA bases in a gene, which produces a genetic variant and can lead to changes in the protein it codes for
what does the shape of a protein determine
its function
what is substitution mutations
when one of the bases in the DNA sequence is changed for another random base
why do mutations sometimes have no effect on the shape or function of the protein
as it does not change the amino acid sequence, as different base triplets can sometimes encode for the same amino acid, so the mutation has no effect on the shape or function of the protein
why do mutations sometimes have an effect on the shape or function of the protein
as the amino sequence has changed and now the protein has a different amino acid
how can mutations affect the non coding part of the DNA
as a gene may be turned on when its supposed to be off, so the cell would produce a protein that its not meant to have at that time
what are groups 3 bases called
codon (which codes for 1 of the 20 different amino acids)
how are proteins made
when amino acids join together and fold into a specific shape
why are insertion mutations harmful
as it causes all the subsequent bases to be shifted along by one which alters all of the subsequent condon, causing the amino acid chain after the point of insertion would be different
how many bases codes for a particular amino acid
3
what are deletion mutations
when a random base is deleted from the DNA base sequence, causing the bases to shift along to the left and this will change way that the base sequence is read and have the same effect as the substitute sequence
what is sexual reproduction
where gentic information from two organisms is combined to produce offspring which are genetically different to either parent
what happens in sexualr reproductions
the mother and father produce gametes by meiosis and the egg form the mum and the sperm cell from the dad fuse together to form a cell with a full number of chromosomes
how many chromosomes do human gametes contain
23
how many chromosomes each do human gametes contain
1
why do offspring inherits features from both parents
as sexual reproduction involves the fusion of male and female gametes so the offspring contains a mixture of their parents genes
why is it good that offspring inherits features from both parents
as the mixture of genetic information produces variation of the offspring
what happens in asexual reproduction
in asexual reproduction there is only one parent so there is no fusion of the gametes, no mixing of chromosomes and no genetic variation between parent and offspring so the offspring are genetically identical to the parent (they are clones)
how does asexual reproduction occur
by mitosis
example of organisms that do asexual reproduction
- bacteria
- plants
- animals
how do you make gametes
cells divide by meiosis
where does meiosis occur in humans
reproductive organs
stages of meiosis
1) before the cell starts to divide it duplicates its genetic information, forming two armed chromosomes, with one arm of each chromosome the exact copy of the other arm and after replication the chromosomes arrange themselves in pairs
2) in the first division in meiosis the chromosome pairs line up the centre of the cell
3) the pairs are pulled apart so each new cell has only one copy of each chromosome
4) in the second division the chromosomes are lined up again in the centre of the cell and the arms of the chromosome are pulled apart
5) you then form 4 gametes, each with a single set of chromosomes in it, each gamete is genetically different from others as the chromosomes all get shuffled u during meiosis and each gamete only get half of them at random
what happens aster two gametes fuse during fertilisation
the produce a new cell which then divides by mitosis to produce a copy of itself, mitosis would then repeat many times to produce lots of new cells in an embryo
what happens when an embryo develops
the cells would then start to diffrentiate into different types of specialised cells that make up a whole organism
advantages of sexual reproduction
- the species can adapt to new environments due to variation, which gives them a survival advantage and are more likely to breed and pass the genes with their characteristics (this is known as natural selection)
- a disease is less likely to affect all the individuals in a population due to variation
- humans can speed up natural selection by selective breeding which allows us to produce animals with desirable characteristics, this means that we can increase food production breeding
disadvantages of sexual reproductions
- time and energy are needed to find a mate
- it is not possible for an isolated individual
what is selective breeding
where individuals with desirable characteristics are bred to produce offspring that have desirable characteristics too
advantages of asexual reproduction
- there only needs to be one parent
- it uses less time and energy as organisms dont need to find a mate
- its faster than sexual reproduction
- many offspring can be produced in favourable conditions
disadvantages of asexual reproduction
- it does not lead to variation in a population
- the species may only be suited to one habitat
- disease may affect all the individuals in a population
what organism can reproduce sexually and asexually
- Malaria - when a mosquito carrying the parasite bites a human, the parasite can be transferred to the human, the parasite reproduces sexually in the mosquito and asexually in the human
- Fungus - species release spores which can become new fungi when they land in a suitable place, spores can be produced sexually or asexually, asexually produced spores form fungi that are genetically identical to the parent fungus, sexually produced spores introduce variation and are produced when there is a change in environment, increasing their chance in survival if the change occurs again
- Plants - flowering plants reproduce sexually as they have egg cells and the pollen acts as sperm whilst strawberries reproduce asexually as they produce runners ( stems that grow horizontally away from the plant) and at various points of the runner a new strawberry plant forms that is identical to the plant
what does the 23rd pair of chromosome determine
your sex
what chromosomes do males have
XY - - they Y chromosome cause male characteristics
what chromosomes do females have
XX - the XX combination cause female characteristics
why is there a 50% of being a boy or girl
as when making a sperm the X and Y chromosome are drawn apart in the first division of meiosis so there is a 50 % chance that a sperm will get a X or Y chromosome, in eggs the original cell has two X chromosomes so all eggs have one X chromosome so when an eggs and sperm fuses there is a 50% chance of getting an XY chromosome or XX chromosome
how are characteristics controlled
by several genes interacting
what are alleles
Alleles are different versions of the same gene
how many alleles are in every gene of the body
2
what is a homozygous gene
two alleles of a gene that are the same
what is a hetrozygous gene
two alleles of a gene that are different
what is a dominant allele
the allele that is always expressed, even if a recessive gene is expressed
what is a recessive allele
the allele that is only expressed if the individual has two copies of itself and does not have the dominant allele of that gene
what is a genotype
the collection of alleles that determine an organism’s characteristics
what is a phenotype
your characteristic
what is cystic fibrosis
a genetic disorder of the cell membrane
what does cystic fibrosis do to the body
causes the body to produce a lot of thick sticky mucus in the air passage and in the pancreas
what are carriers
people with only one copy of the recessive allele that dont have the disorder
what does it take for a child to have cystic fibrosis
both parents must be either carriers or have the disorder themselves
what is the dominant allele for cystic fibrosis represented as
F
what is the dominant allele for cystic fibrosis represented as
F
what is the recessive allele for cystic fibrosis represented as
f
how many people carry cystic fibrosis
1 in 25
what is polydactyly
a genetic disorder where a babys born with extra fingers or toe
what is cyctic fibrosis caused by
the recessive allele
what is polydactyly caused by
the dominant allele
what is the dominant allele represented as in polydactyly
D
what is the recessive allele represented as in polydactyly
d
what causes a child to have polydactyly
if one of the parents carries the condition
how are embryos screened before IVF
- before the embryo is implanted into the mother’s womb the doctor would remove a cell from the embryo and analyse its genes to detect genetic disorders
what happens to the embryos with gentic disorders for IVF
the embryos would be destroyed
what happens to the embryos with gentic disorders for embryos in the womb
could lead to the decision to terminate the pregnancy
advantages for embryo screening
- it would help to stop people suffering
- treating disorders costs the government money
- there are laws to stop it going to far
disadvantages for embryo screening
- it implies that people with genetic problems are undesirable and this could increase prejudice
- there may come a point where everyone wants to screen their embryos so they can pick the most desirable one
- screening is expensive
